In a continuously variable transmission (CVT) used in an automobile and the like, a CVT fluid (oil) is supplied to a part to be lubricated requiring oil for lubrication, power transmission, cooling, and the like by an oil pump, as well as to an hydraulic control part requiring oil for transmitting an oil pressure in controlling a transmission gear ratio by an oil pressure.
The oil to be supplied is collected by a collecting part such as an oil pan provided at a bottom of the CVT, for example. The oil collected by the collecting part is fed again into the part to be lubricated and the hydraulic control part by the oil pump.
For example, in a case where the part to be lubricated of the CVT is rotated at a high speed and the like, bubbling occurs to the oil fed into the part to be lubricated.
In a case where an air bubble is mixed in the collected oil due to the bubbling and other reasons, an operational failure and a drop in the oil pressure may occur as a result of air entrainment by the oil pump, which has sucked the collected oil.
That is, the oil pressure in the hydraulic circuit may become unstable.
Therefore, it is proposed that a hydraulic circuit for transmissions, for example, is provided with a main oil pathway, through which oil is circulated by a main pump and is fed into a hydraulic operation part operated by an oil pressure, and with a separately-provided sub pump (see, for example, Patent Literature 1).
In Patent Literature 1, the oil is fed into the hydraulic operation part through the main oil pathway by the main pump, and when the oil pressure drops in the main oil pathway, oil is supplied to the main oil pathway by the sub pump, whereby it is possible to prevent a drop in the oil.
Furthermore, oil that has been discharged accompanying operation of the hydraulic operation part is recirculated, for example, in another part requiring the oil.
At this time, a destination for discharging the oil to be excessive is a position where only the sub pump can suck the oil.
At this position, there is a fear that the oil may contain an air bubble caused by discharging the oil to be excessive.
Therefore, the oil containing an air bubble is sucked on the sub pump side, whereby it is configured such that the main pump does not easily suck an air bubble.
Accordingly, intrusion of an air bubble into the main pump and the main oil pathway side can be suppressed.
Furthermore, there is proposed an oil strainer, arranged on a suction side of an oil pump for a transmission, for suppressing intrusion of an air bubble into the oil pump side while achieving downsizing (see, for example, Patent Literature 2).
Furthermore, a proposal has been made, although not for removing an air bubble, for improving a lubrication performance and a cooling performance of the part to be lubricated by spraying oil mist, which is a mixture and an atomization of oil and air, to apart to be lubricated (see, for example, Patent Literature 3).